Near-field photolithographic masks and photolithography; nanoscale patterning techniques; apparatus and method therefor

ABSTRACT

A new field of technology, near-field photolithography, is proposed. In near-field photolithography, an opaque pattern having a nanoscale resolution is made using a modified scanning tunneling microscope to deposit the opaque material on an electrically conductive material. A transparent sheet of indium tin oxide is patterned with a plurality of opaque copper deposits having a nanoscale resolution. The patterned indium tin oxide is then used as a photolithographic mask in the optical near-field. Near-field resolution is not diffraction limited, and near-field photolithography is able to pattern objects with sub-wavelength resolution. As a result, smaller semiconductor microchips can be manufactured and a new nanotechnology, e.g., nanomachines, can be developed. The scanning tunneling microscope (STM) is used as an &#34;electrochemical paintbrush&#34; to transfer the copper from a massive copper supply to the STM electrode tip and then to the ITO surface without degrading the STM tip.

FIELD OF THE INVENTION

The present invention is directed to improvements in photolithography,more particularly to a nanoscale photolithographic mask, methods andapparatus for forming such masks, and near field photolithography usingsuch masks, for example, in semiconductor processing and integratedcircuit manufacture. The invention also has application toelectroplating and electromilling of electrically conductive materials.

BACKGROUND OF THE INVENTION

Present commercial photolithography, more particularly photolithographyfor use in semiconductor processing, uses light to expose a substratecoated with a photosensitive material (also known as a "resist" coating)through a mask. The mask has an opaque pattern that blocks some of thelight. The "resist" material that is sufficiently exposed to the lightnot blocked by the mask acquires a characteristic that is different fromthe resist that is blocked by the mask from the light. As a result, theexposed resist can be "developed," that is physically removed by achemical processing to expose the substrate. The substrate is thenprocessed by a semiconductor processing step, e.g., doping the exposedsubstrate with an "n" or a "p" material, or oxidizing the exposedsubstrate, it being understood that other processing treatments could beapplied in a conventional manner. The portion of the substrate thatremains coated by resist remains comparatively unaffected by thisfurther processing. Then, the so-processed substrate is furtherprocessed to remove the remainder of the resist coating, leaving thesubstrate having an n, p, or oxidized material formed therein in thepattern of the mask. Thereafter, another resist coating may be applied,a different mask used to expose the resist and a different pattern of nor p material, or oxidation is formed in the substrate to form adifferent layer of material. By this technique of repeatedphotolithographic exposure through a mask and processing, thesemiconductor material is formed into an integrated circuit (morespecifically a plurality of integrated circuits) as is well known.Although the present invention is by no means limited to semiconductorprocessing to form integrated circuits, such techniques provide a usefulframework for understanding the invention, as discussed below.

Current photolithography has a resolution with dimensions on themicrometer level. Stated otherwise, the smallest dimension of a line(such as a wire or lead connecting two circuit elements) that can bemade using photolithography is approximately 0.2 micrometers. Thisdimensional limit controls the size of the circuit elements used in thesemiconductor chip, and thus how many circuits can be formed in a givenamount of real estate (circuit density). This in turn affects the costof integrated circuits as well as the speed at which the circuits canoperate and how much power is needed to operate the integrated devices.

Current efforts are being made to increase the resolution to below themicrometer level, more specifically, to the nanometer level. Advances,however, have been limited by the physics of light scatter anddiffraction attributable to the wavelength of the light radiation usedto expose the resist coated substrate through the mask. In this regard,the photolithographic masks are used in the far-field and conventionaland commercial photolithographic techniques for manufacturing integratedcircuits are Abbe-diffraction limited in their achievable resolution.This limits the size of features to be patterned on the substrate(namely, the semiconductor chips) to one-half the wavelength of thelight used. Currently, the resolution is limited to a minimum dimensionof about 0.2 micrometers. Attempts to move to shorter wavelengths oflight have not shown much success. See, e.g., "The limits oflithography" Scientific American (September 1995), p. 66; and Stix,"Toward `point one`" Scientific American (February 1995), pp. 90-5.

Due at least in part to the difficulties in improving resolution inphotolithography, there also has been considerable activity usingalternate techniques for forming masks and patterns in substrates forsemiconductor processing. These include electromagnetic radiation in thex-ray region and electron beams. Although these technologies have metwith some technical success, they involve other considerations, inparticular time and cost, in their implementation that have inhibitedwidespread adoption of the technology, and, to date, preventedimplementing forming masks and patterns with sub-micrometer resolutionin mass production. The term "nanoscale" as used herein means adimensional resolution of a pattern or a structure that issub-micrometer, more preferably less than 0.2 micrometers in resolution.

There also exists a device known as a scanning probe microscope in whicha high-precision actuator moves a miniature sensor over the surface of asample. See, for example, Jefferson, "The imaging of individual atoms",Science, V. 274 (Oct. 18, 1996), p. 369. Because the sensor and thesample interact only over a very small area, the scanning probemicroscope attains a high resolution that can image nanoscalestructures. Among the many types of scanning probe microscopes whichhave been built are scanning tunneling microscopes ("STM"), atomic forcemicroscopes, scanning electrochemical microscopes ("SECM") and scanningnear-field optical microscopes. See, generally, Dror, Scanning ForceMicroscopy: With Applications to Electric. Magnetic, and Atomic Forces,Oxford University Press, (New York, 1991).

A scanning tunneling microscope (STM) senses quantum tunneling ofelectrons. Electrons tunnel between an atomically sharp wire tip and anelectrically conducting sample. A piezoelectric ("piezo") transducerscans the tip across the surface of the sample in a raster pattern. Inone implementation, the resulting changes in tunneling current arerecorded. However, it is more common to use a negative feedback loop tovary the height of the tip in response to minute changes in thetunneling current. This keeps the tip's height above the sample, and thetunneling current, constant. The output of the feedback loop also givesa measure of the height of the sample's surface. This is described inBinnig et al., "Surface studies by scanning tunneling microscopy"Physical Review Letters, V. 49 (Jul. 5, 1982), pp. 57-61.

The tunneling current falls off exponentially as the distance betweenthe tip and the sample increases. It has been demonstrated that,typically, the tunneling current decreases by about an order ofmagnitude for each additional Angstrom of separation between the sampleand the tip. Guntherodt et al. (eds.), Scanning Tunneling Microscopy I,(Springer-Verlag, New York, 1992) ("Guntherodt"). This leads to theextremely high resolution of an STM.

STM theory is treated more fully in the published literature. See, e.g.,Guntherodt; Volodin, "Tactile microscopes" Quantum, V. 3(January/February 1993) pp. 37-40; Binnig et al., "Vacuum tunneling"Physica, 109 & 110B (1982) pp. 2075-2077; Binnig et al., "Surfacestudies by scanning tunneling microscopy" Physical Review Letters, V. 49(Jul. 5 1982) pp. 57-61; and Dror, Scanning Force Microscopy: WithApplications to Electric, Magnetic, and Atomic Forces (Oxford UniversityPress, New York, 1991). The reader is referred to each of the foregoingreferences for further details on STM design theory and applications.

One proposal to solve the problem of increasing the feature density onsilicon wafers is the use of scanning tunnelling microscopes ("STMs")and atomic force microscopes (AFMs) to pattern the surface directly.See, for example, Zhang et al., "Creation of nanocrystals through asolid-solid phase transition induced by an STM tip," Science, V. 274(Nov. 1 1996), pp. 757-60; and "Atomic landscapes beckon chip makers andchemists," Report from the American Vacuum Society Meeting, Science, V.274 (Nov. 1 1996, pp. 723) (the "AVS Report"). It has been shown thatthese microscopes can manipulate individual atoms to create nanoscalestructures. Unfortunately, these microscopes are too slow to create themillions of integrated circuit chips, each with millions of transistors,required by the semiconductor industry. Attempts to create AFMs withmultiple tips working in parallel have shown only limited success, asnoted in the aforementioned AVS Report.

SUMMARY AND OBJECTS OF THE INVENTION

It is, therefore, an object of the invention to overcome the foregoingproblems and achieve photolithography with improved resolution on ananoscale dimension.

It is another object to provide a nanoscale mask for photolithography.

It is another object to provide apparatus and methods for creating ananoscale mask for photolithography.

It is another object to provide near field photolithography for formingnanoscale patterns or structures.

It is another object of the invention to provide an electrochemicalpaintbrush that can be used to deposit on or remove from a conductivesurface a material on a nanoscale dimension as well as on largerdimensions.

The present invention concerns developments related to a new field oftechnology, namely near-field photolithography, in which a pattern,opaque to the illuminating electromagnetic radiation, having a nanoscaleresolution is made using a modified scanning tunneling microscope. Theopaque material, preferably an electroplatable metal, is deposited on anelectrically conductive material, e.g., a transparent sheet of indiumtin oxide, as a plurality of deposits or "dabs" of the opaque material,having a nanoscale resolution. The patterned indium tin oxide is thenused as a photolithographic mask in the optical near-field. Near-fieldresolution is not diffraction limited, and near-field photolithographyis able to pattern objects with sub-wavelength resolution. As a result,smaller semiconductor microchips can be manufactured and a newnanotechnology, e.g., nanomachines, can be developed.

The scanning tunneling microscope (STM) is used as an "electrochemicalpaintbrush" to transfer the electoplateable material from a massivecopper supply to the STM electrode tip, and then to the ITO surface.This occurs cyclically in an aqueous electrolyte solution of theelectroplatable material, without degrading the STM electrode tip, andwhile maintaining the ion concentration of the opaque material in thesolution constant.

The cycling can be reversed so as to remove an amount ofelectroplateable material from a specific area of a conductive surface,for example, to repair or modify a previously made nanoscalephotolithographic mask, or to mill a portion of a conductive structure.The removed portion can be deposited on the massive supply or on adifferent area of the conductive surface. By selection of the currentand other electroplating parameters, amounts of electroplatablematerial, from nanoscale to centimeter scale, can be deposited orremoved, depending on the polarity of the current flow and the desiredresult. Above the nanoscale range, the STM and electrochemical tip asdescribed herein can be replaced with a suitable inert electrode.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features of the invention, its nature and various advantageswill be apparent from the accompanying drawings and the followingdetailed description of the invention, in which like reference numeralsrefer to like elements, and in which:

FIG. 1 is an elevated perspective view of an apparatus, including ascanning tunneling microscope (STM), and control circuits, for use informing nanoscale photolithographic masks in accordance with a preferredembodiment of the present invention

FIG. 2A is a circuit schematic diagram of a z-piezo feedback circuit ofthe control circuit of FIG. 1;

FIG. 2B is a circuit schematic diagram of a raster scan generator of thecontrol circuit of FIG. 1;

FIG. 2C is a circuit schematic diagram of a computer interface betweenthe STM and the computer of FIG. 1;

FIG. 3 is a graph showing two representative plots of the power spectraldensity of tunneling current noise, the top plot being without activefeedback and the lower plot being with active feedback, the plots havinga logarithmic y-axis in power and a linear x-axis of frequency in Hertz;

FIG. 4 is a schematic drawing of a prior art process for forming a tipof the STM of FIG. 1 in accordance with the present invention;

FIG. 5 is a circuit schematic diagram of an electrochemical paintbrushcontrol circuit in accordance with an embodiment of the presentinvention;

FIGS. 6 and 6A are schematic drawings of a process for depositing anopaque material using the electronic paintbrush control circuit of FIG.5, in accordance with an embodiment of the present invention;

FIG. 7 is a graph showing a calculated simulation of copper deposition,having units of distance along the ITO on the x axis and height of thedeposition along the y axis;

FIGS. 8A and 8B are respectively scans of an ITO surface before andafter deposition of copper; and

FIGS. 9A and 9B are respectively illustrations of prior artphotolithography and near-field photolithography.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIGS. 1 and 2, in accordance with the preferred embodimentof the present invention, an apparatus for forming nanoscalephotolithographic masks is shown. The apparatus includes an STM 100comprising a mechanical structure and is operated by a computer 20executing control software and control electronics 300.

Scanning Tunneling Microscope

Referring to FIG. 1, the mechanical structure of an STM 100 includes astage 110 for supporting a sample 10, a piezoelectric actuator 140 onwhich a tip 130 is mounted, a coarse adjustment and a fine adjustmentfor positioning the stage 110 relative to tip 130, and a housing orframework (not shown) on or to which the various components are mounted.The STM 100 is designed to work under ambient conditions and in anelectrochemical environment and has two operating requirements. First,the stage 110 must be adjustable to a precision that is within a fewhundred nanometers. Second, the STM 100 must be immune to vibrationsfrom the environment.

The mechanical structure of the STM 100 by be any suitable materialhaving a suitable structural rigidity to support the components andshield the sample 10 from ambient air currents. A conventional STM maybe purchased, e.g., model Nanoscope I, II or III available from DigitalInstruments. Alternately, one may be constructed using for structure,for example, a rigid plastic, such as a polyethylene, polycarbonate orpolyurethane, or a metal such as stainless steel or a low thermalexpansion alloy. An experimental prototype STM 100 was constructed usingLEGO® building blocks (LEGO is a registered trademark of Interlego AG).

In a preferred embodiment, the stage 110 of STM 100 rests on threefine-pitch screws 112(a-c). Two of the screws 112a, 112b, can bemanually turned for achieving a coarse adjustment of stage 110. By soadjusting these screws, it is possible to position the sample 10 towithin about 5 micrometers of the tip 130. The third screw 112c isconnected to a gear chain 114 which has a turning knob 115 on the end ofthe gear chain. The gear chain 114 is dimensioned so that a set numberof rotations of the knob 115 causes one rotation of the screw 112c. Thisscrew 112c, therefore, can be used to position finely the stage 110 towithin about 100 nanometers of the tip 130. In the experimentalprototype, 675 rotations of knob 115 resulted in one rotation of screw112c. A conventional gear reduction system made from Lego, blocks wasused in the experimental prototype, and any coventional system may beused in place of a chain driven system.

A piezoelectric actuator ("piezo") 140 is rigidly mounted to the frameand located above the stage 110. The piezo 140 is controlled to move thetip 130 in each of the x, y, and z directions (or axes), with asensitivity of 34 angstroms/volt. As shown in FIG. 1, the piezo 140 mayactually comprise three separate and independently controllable piezos140x, 140y and 140z for controlling motion in the x, y and z directions,respectively. Although not shown, each piezo element 140x and 140y mayhave two such pieces disposed on axis, symetrical about the z axis.

To isolate against high frequency vibrations, the entire STM 100 frameis encased in about 7 kilograms of plasticine (a kind of modeling clay(not shown)). In addition, bungee cords (not shown) are used to suspendthe STM 100 frame from a structure, such as a concrete ceiling, toisolate the STM 100 from low frequency vibrations. Bungee cords areelastic cords used to secure items from movement and are available atsporting goods and luggage stores. Other forms of mechanical vibrationisolation could also be used.

Referring to FIGS. 1, 2a and 2c, control software suitable for operatingthe STM 100 may be custom written, for example, in the QBasicprogramming language. In addition, a data analysis software routine maybe written in the Matlab programming language. The specific programs maybe designed in any of a number of ways, within the abilities of a personof ordinary skill in the art.

The control software thus provides a program that functions to monitorin real time the x, y, and z coordinates of the tip 130, the biasvoltage V_(B) applied between the tip 130 and the sample 10, a desiredtunneling current IT which is set manually using a potentiometer P2, andthe actual tunneling current I_(Tact). The software is preferablywritten to record data in either a constant height mode or in a constantcurrent mode. The data analysis software includes routine functions toprocess the data and display the results of the scans (see FIGS. 3, 8A,8B), and can preferably perform a Fourier analysis to try to separatethe signal from the noise. A monitor 21 and/or a printer 22 can beconnected to computer 20 to display and or printout the recorded data.

Referring now to FIGS. 1, 2A-2C, the control circuit 300 includes az-piezo feedback circuit 330 which functions to maintain a steadytunneling current I_(Tact), a raster scan generator 360 which functionsto move the tip 130 in a desired raster scan, e.g., in the x and ydirections, and a computer interface 380 which functions to acquire datafor monitoring and/or controlling the operation of STM 100.

Referring to FIG. 2A, the z-piezo feedback circuit 330 monitors theactual tunneling current I_(Tact) and adjusts the vertical position, inthe z axis, of the tip 130 to try to maintain the tip 130 apredetermined distance, that is a constant height, above the sample 10,and thereby to maintain a steady tunneling current I_(Tact). Circuit 330includes a bias voltage amplifier A1 coupled to the tip 130, apreamplifier A2 coupled to the sample 10, an amplifier gain stagecomprising amplifiers A3 and A4 coupled to the preamplifier A2, areference current signal provided by amplifier A5, an error signaldifferential amplifier A6, and an RC integrating amplifier A7. AmplifierA1 is a preferably a model LM324 operational amplifier ("op-amp") whichfollows the voltage set on potentiometer P1, (a 5K potentiometer) by the+12 v source, allowing a bias voltage V_(B) of between 0 V and +10 V tobe applied to the tip 130. The bias voltage V_(B) is measurable at nodeA. Typically, bias voltages range from 100 mV to 2 V. A switch SW1 isprovided along with three resistors R10, R20, R30 to connect selectivelythe sample 10 to ground to convert the tunneling current I_(Tact) into avoltage V_(B) to be measured by amplifier A2, e.g., a high-impedanceJFET op-amp (model LF 353). The three resistors R10, R20, R30,respectively 1K, 10K and 100K, do not appreciably alter the voltage dropV_(B) between the tip 130 and the sample 10 because a maximum tunnelingcurrent of 10 nA would only generate a 1 mV drop across the 100Kresistor R30.

Amplifier A2 amplifies the current signal I_(Tact) by a factor of 101through use of a resistor divider R101 (1K) and R102 (100K) in thefeedback loop, and amplifier A3 further amplifies the signal by a factorof -100 using resisters R104(1K) and R105 (100K), and a 12 v sourcesupplied across resistor R103 (1M) is added to the output of amplifierA2. Amplifier A3 also is preferably a model LF353 op-amp. Amplifier A4(model LM324) inverts the signal with unity gain (using resistors R106and R40 (each 47K)), returning it to its original polarity. Throughresistor R40 and diode D1 (model 1N914) in the feedback loop, amplifierA4 also removes the positive part of the signal output from amplifierA3. This is because any positive signal from amplifier A3 must come fromnoise and is therefore to be suppressed.

The goal tunneling current I_(T) is set using potentiometer P2 (a 5Kpotentiometer coupled to +12 V), and amplifier A5 (a model LM324op-amp). The goal current I_(T) is measurable at node C at the output ofamplifier A5. Amplifier A5 also is configured with resisters R107(19K)and R108(1K) to scale its output to appropriate values. Amplifier A6 (amodel LM324) subtracts the signal from amplifier A5 output across aresister divider of resistors R111 (15K) and R112 (15K), representingthe goal current I_(T), from the signal I_(Tact) across the voltagedivider of resisters R109 (15K) and R110 (15K), representing the actualtunneling current. Thus, the output of amplifier A6 is a measure of theerror in the tunneling current. This error signal is passed to theintegrator amplifier A7, a model 741 op-amp having a 0.1 μf capacitor C1in the feedback loop, and a potentiometer P3 at the inverting input anda resistor R50 (100K) at the noninverting input. The integrator A7 thushas a variable time-constant, which is set by adjusting potentiometerP3. Too high a time-constant leads to an unstable tunneling current,while too low a time-constant can lead to oscillations. The ideal valueof the time-constant is to be empirically determined, and depends on theamount of acoustical noise and the conditions of the tip 130 and sample10. These factors can change from minute to minute as well as fromsample to sample. Computer 20 can be programmed to adjust digitallypotentiometer P3 as appropriate, to maintain an appropriate timeconstant.

The output of the integrator A7, which is measurable at node D, drivesthe piezo 140 in the "z" direction. This moves the tip 130 toward oraway from the sample 10 in the z axis. If the tunneling current I_(Tact)is too high, the integrator A7 operates to draw the tip 130 away fromthe sample 10; if the tunneling current I_(Tact) is too low, the tip 130is moved closer to the sample 10. FIG. 3 shows the effect of the activefeedback circuit 330, on the electrical noise in the tunneling current.It is noted that the use of the feedback loop decreases the power of thenoise by a factor of approximately 61.

Referring to FIG. 2B, the raster scan generator circuit 360 produces araster pattern of motion in the x and y directions, similar to the scanlines on a television screen. Raster scan generator circuit 360generally has two triangle wave generators, one for controlling motionin each of the x and y directions, which have different operatingfrequencies. This is so that the tip will traverse the y dimension rangebefore it is advanced in the x direction. Polarity inverter amplifiersare respectively connected to the triangle wave generators to obtainboth x and y direction motion control signals of opposite polarity tocontrol piezo 140.

In a preferred embodiment, the triangle wave generator is constructed ofamplifiers A8 and A9 (models LM324 op-amps) configured with resistorsR210 (15K) and R212 (10M) and capacitor C210 (0.7 μf) to produce a lowerfrequency triangle wave which drives the piezo 140 in the x-direction.The output of amplifier A9 is measurable at node E. The low frequencymay be from 1 to 0.01 Hz, more preferably 0.1 Hz. Amplifiers A11 and A12similarly combine with resistors R310 (15K) and R312 (1.0M) andcapacitor C310 (0.1 μf) to produce a higher-frequency triangle wave todrive the piezo 140 in the y-direction. The output of amplifier A11 ismeasurable at node F. The higher frequency may be from 1 to 100 Hz, morepreferably 10 Hz. The outputs of the two triangle-wave generators arerespectively inverted by amplifiers A10 and A13 (each model LM324)having a gain of -1 using resistors R214 and R215, and R314 and R315(15K each).

The outside of the piezo 140 is divided into four quadrants 140x+,140x-, 140y+, 140y-. In the x and y directions, opposite quadrants ofthe piezo 140 (x+ and x-) and (y+ and y-) are driven by triangular wavesignals of opposite polarity. This prevents the piezo 140 from moving inthe z-direction in response to the signals intended to move it in the xand/or y directions.

Referring to FIG. 2C, to record data from the STM 100, a special-purposecomputer interface 380 was designed and built, although a commerciallyavailable interface also could have been used. The computer interface380 may be of any construction which allows the computer 20 to monitorseveral parts of the STM control circuit 300 in cooperation with thecontrol and data acqusition software. Computer 20 is a conventionalpersonal computer, e.g., a 486 or Pentium class microprocessor basedsystem having a keyboard, printer, mouse, display and disk drives.

The computer interface circuit 380 has a decoder circuit 383 whichfunctions in a conventional manner to decode an address signal from thecomputer bus 382 on address lines A0-A7. The decoder circuit 383includes And gates G1, G2, G3, G4 and G5, and inverters I1, I2, I3, I4and I5, which are configured as shown to decode the address as describedherein. If the address is correct (H2FF) and the Input/Output Write("IOW") line 384 is asserted low, the computer 20 sends a control wordto the interface 380 on bus 379 (data lines DO-D7). In the designedembodiment, 8 bit words are used. Data bits 0,1 and 2 of the controlword determine the state of the 8-channel analog multiplexer 386. Asuitable multiplexor device is a model 4051 available from NationalSemiconductor. The multiplexer 386 switches one of the signals from thesix monitoring nodes A, B, C, D, E and F in the circuit 300 (see FIGS.2A and 2B) through the signal conditioning input port 378 to the inputof an analog-to-digital converter (A/D) 388. A/D 388 may be, forexample, a model ADC0804LCN device. The six nodes provide the x (nodeE), y (node F), and z (node D) coordinates of the tip 130, the biasvoltage V_(B) (node A), the desired tunneling current I_(T) (node C),and the actual tunneling current I_(Tact) (node B).

A data latch 385 is interposed between, on the one hand, data bus 383,and, on the other hand, the control inputs of analog multiplexor 386, anA/D range select circuit 389, and an A/D offset select circuit 387. Thelatter two circuits are used to control the range and offset operationof multiplexor 386.

In a preferred embodiment, the control data word includes bits to selectthe range and offset of the voltages that the A/D 388 is able toconvert. Data bits 3, 4 and 5 of the control data word are used toselect from among eight possible A/D input ranges. The values of theranges are selected in circuit 389 by varying potentiometers P4, P5 andP6 (each being a 100K potentiometer connected to the data bits 3, 4, 5respectively, with the outputs being summed by amplifier A18 (a modelLM324 op-amp) and inverted by amplifier A19 (a model LM324 op-amp)having unity gain by use of resisters R400 and R401 (3.9K each). Aresister R402 of 3.0K is applied in the feedback of amplifier A18.

In offset select circuit 387, data word bits 6 and 7 are input and usedto select from among four A/D offset voltages. This is achieved byselectively combining resistors R403 and R404 having 10K and 18Krespectively, as selected by the value of data bits 6 and 7. The outputsare summed at the inverting input of amplifier A20 (a model LM324op-amp) and inverted by amplifier A21 (a model LM324 op-amp). A 5.1Kresistor R405 is in the feedback of amplifier A20, and amplifier A21 hasresistors R406 (8.2K) and R407 (10K) coupled to the inverting input asshown in FIG. 2C.

Thus, under software control, by appropriate selection of circuitelement values, the computer 20 can digitize signals in almost any rangewith a full eight bits of resolution. The computer 20 also can usedifferent range and offset values for each of the six signals that thecomputer 20 monitors. It should be understood that the potentiometersP4-P6 may be digitally controllable devices.

When the computer address bus 382 presents address H2FF and the IORInput/Output Read ("IOR") line 390 is asserted low, the A/D 388 sends tothe computer data bus 381 the digitized value of the selected analogvoltage at its input.

As will be appreciated by persons skilled in the art, the circuitconfiguration and component values selected in the exemplary embodimentdescribed above can be modified in numerous ways to obtain the sameresults, and further, that different circuit elements, devices andstructures can be connected to achieve the same performance or resultsas in the exemplary embodiment depicted in FIGS. 2A-2C and describedherein. It also is noted in the drawings depicted that +12 v is used asa supply voltage, the operational amplifiers are biased between +12 vand -12 v, and the digital circuit chips are driven by +5 Vcc andgrounded, which voltages, V, Vcc, and ground connections are not alwaysshown for clarity of presentation.

It is noted that the experimental prototype STM 100 described above wasdesigned and constructed with most of the features of a commerciallyavailable device, but cost approximately $50 to build (excluding thecost of computer 20, piezo 40, the LEGO blocks, and software licenses).The STM 100 succeeded in generating the pictures depicted in FIGS. 3, 8Aand 8B. Further, it is noted that some of the analog signal processingcould be performed digitally under software control and processing ofthe digitalized data, provided that the software has sufficient speedand power.

Copper Deposition on Indium Tin Oxide

The STM 100 described above is provided with a tip 130 that is suitableto perform electrochemical studies. Nichols, "Scanning probe microscopystudies of copper electrodeposition," Gewirth et al., Nanoscale Probesof the Solid/Liquid Interface, (Kluwer Academic, Boston, 1995), pp.163-182; and Wenjie Li et. al., "Electrochemical deposition of metalnano-disk structures using the scanning tunneling microscope," Gewirthet al., Nanoscale Probes of the Solid/Liquid Interface, Kluwer Academic,(Boston, 1995), pp. 183-192. In accordance with the present invention anelectrochemical paintbrush control circuit 500 also is provided tocontrol the operation of STM 100 with the electrochemical tip 130. TheSTM 100 was then used to electroplate copper from a copper sulfatesolution onto an indium tin oxide ("ITO") sample, as will be presentlydescribed.

It is recognized that when a conventional STM electrode having atungsten tip is immersed in an electrolytic solution, ionic currentscompletely swamp any tunneling current (See Gewirth et al., NanoscaleProbes of the Solid/Liquid Interface, (Kluwer Academic, Boston, 1995).Ionic currents are not limited to the few atoms at the very end of thetip, but can flow from any part of the electrode that is in contact withthe solution. Thus, the STM tungsten tip loses all spatial resolutionwhen placed in an electrically conducting liquid.

This obstacle is overcome in the present embodiment by use of a tip 130adapted for electrochemical applications (also called an"electrochemical tip"). In this regard, a platinum wire is used in placeof the standard tungsten in the tip 130 of the original STM, becauseplatinum is relatively inert in electrochemical solutions. Othersimilarly inert metals could be used.

More specifically, referring to FIG. 4, an electrochemical tip 130 isprepared by obtaining a platinum wire 131, which is provided with anatomically sharp point or a close to atomically sharp point (step 1) anddipping the point in hot paraffin 132 (step 2), so that the end of thewire 131 acquires an insulating coating of paraffin 132 (step 3). Theinsulated platinum electrode 130 is then mounted on the piezo actuator140 of STM 100.

A peltier thermoelectric module 600 is then mounted on the stage 110 andthe paraffin coated tip 130 is brought into contact with module 600(steps 3, 4). Module 600 heats the paraffin 132 around the platinum tip130. The top of the peltier thermoelectric module 600 is covered withaluminum foil 610, which is connected to the input of a current sensingpreamplifier 625. The paraffin-coated tip is slowly pushed into the topof the thermoelectric module 600 (step 4). This may be done manually orunder piezo control. The heat from the peltier module 600 makes theparaffin pliable. As soon as the platinum wire 131 pokes through theparaffin 132, current flows from the platinum tip 130, through thealuminum foil 610 on top of the heater 600, and into the preamplifier625 which produces an output indicative of the current flow e.g.,illuminates an LED or light bulb. The thermoelectric module 610 is thenimmediately shut off and the tip 130 is advanced no further.

This procedure leaves almost the entire wire 131 covered with aninsulating layer of paraffin 132. Only a tiny area on the tip 130 of theplatinum wire 131 is left exposed. Since ionic currents can only flowfrom the tip of the exposed wire 131, the spatial resolution of the STM100 is thereby maintained in an electrolytic solution. (See, e.g.,Fu-Ren Fan et al., "Single Molecule Electrochemistry", Journal of theAmerican Chemical Society, V. 118, (Oct. 9, 1996) pp. 9669-9675.

The STM 100 of the present invention is advantageously used to depositan opaque electroplatable material on a sample that has an electricallyconductive surface, such as ITO. It should be understood, however, thatvirtually any electrically conductive material may be used in place ofITO. To create a nanoscale photolithographic mask, in accordance withthe present invention, it is important to keep the opaque deposituniform, and to achieve this in the electrochemical system it isnecessary to maintain a constant concentration the ionic form of theopaque material in the electrochemical plating solution 50. Asrecognized by the inventor, where the opaque material selected iscopper, which example is used in the discussion following, if the anodein an electroplating bath of, e.g., copper sulfate is made of copper,copper from the anode will go into solution to replace the copper beingdeposited on the cathode, namely the electrically conductive surface 12of sample 10. However, an STM tip made of copper would not work well inthis situation because the tip would gradually dissolve in use.

To circumvent this problem, with reference to FIG. 5, a large copperelectrode 700 is placed in the solution 50 along with the platinumelectrochemical tip 130 and the indium tin oxide (ITO) layer 12 ofsample 10. The electrochemical paintbrush circuit 500 functions to keepthe copper ion concentration constant, while allowing precise control ofthe deposits. It does so by controlling the electroplating current sothat the net current flow out of tip 130 is zero (or negligible).

In a preferred embodiment, the circuit 500 has two modes of operationand the operating mode is selectable by a switch SW2. Switch SW2 may beoperable manually or under computer control. In the first mode, if theswitch SW2 is open (o), no copper is deposited anywhere. In this mode,the circuit 500 merely monitors the electrical resistance of thesolution 50. If the switch SW2 is closed (c), then in a first phasecurrent and copper ions flow from the large copper electrode 700 to thetip 130, and in a second phase current and copper ions flow from the tip130 to the ITO 12. With the switch SW2 closed, the platinum tip 130 actslike a paintbrush: the tip 130 picks up an amount of copper from thecopper electrode 700 and then electrochemically transfers it to the ITO12, without being permanently changed by the electrochemical process.This advantageously prevents degradation of tip 130 and permits the useof a large mass of copper in electrode 700.

When SW2 is in the open position, the circuit is functionally the sameas the triangle-wave generating circuits illustrated in FIG. 2B anddescribed above. As a result, an alternating current flows through theplatinum electrode 130. Any electrochemical reaction which takes placeduring one half-cycle of the current flow is reversed during the otherhalf-cycle. Thus, there is no net reaction.

With SW2 closed, the circuit 500 is in its second or painting mode. Withreference to FIGS. 5, 6 and 6A, in phase A when the output of amplifierA30 (a model LM 412 op-amp) is high, the large copper electrode 700becomes an anode, the platinum tip 130 a cathode, and the ITO 12 isdisconnected (isolated from the electrochemical system). A small amountor "dab" of copper 701 is transferred over time from the copperelectrode 700 to the platinum tip 130 by action of an ionic currentI_(ion) (FIG. 5). More specifically, copper from copper electrode 700goes into solution and copper ions in the solution plate out on tip 130.Amplifier A30 functions to measure the charge flowing into the platinumelectrode. Once a certain amount of charge has flowed, comparator A40 (amodel LM 311 comparator) switches states. The amount of charge, andhence the amount of copper 701 (that is, the size of the dab), can beselected by appropriate choices of the circuit and electrochemicalparameters, as will be explained. Thus, at the end of phase A, whenamplifier A40 goes low, phase B begins, the copper electrode 700 isdisconnected, the STM tip 130 becomes the anode, and the ITO coating 12becomes the cathode. The dab of copper 701 on the STM tip 130 then goesinto solution, while a dab 702 of equal size is deposited on an area ofITO 12 that is proximate to tip 130. This circuit 500 provides that theaverage current flow out of the STM tip 130 is 0, and that theconcentration of the copper sulfate solution remains constant.

The number of moles of copper deposited as a dab 701 or 702 during eachcycle is given by the formula: ##EQU1## where n is the number of molesof copper deposited, Vs is the supply voltage of the comparator, F is96,500 (the number of coulombs in a mole of electrons), and C and R_(x)refer to the capacitor and resistors on the circuit diagram illustratedin FIG. 5. If Vs=10 V, C=1 nf, R₁ =R₄ =1K, R₃ =10K, and R₂ =100K, eachcycle will deposit 4.7×10⁻¹⁷ moles of copper. This small quantitydeposits a dab 702 that is approximately 70 nm across and should allowextremely high-resolution (nanoscale) patterning of the ITO surface. Theperiod of each deposition cycle is proportional to R₅ and R₆, andinversely proportional to C. A calculated cross-section of a copperdeposit on ITO for four successive current phases is shown in FIG. 7.The units are arbitrary and show the height (y-axis) vs. distance alongthe ITO (x-axis). A suitable range of copper dabs to be deposited percycle is 1×10⁻¹⁷ to 1000×10⁻¹⁷ moles. Thus, in patterning a surface asingle dab 702 may be applied to a given area of the ITO 12, or multipledabs 702 can be applied to the same area, whether or not the multipledabs 702 are deposited in succession.

This setup benefits from both the high resolution of the platinum tip130 and the large reservoir of copper in the copper electrode 700.Inspection with an optical microscope verified that the experimental tip130 was not affected by this cyclic transfer process, which is alsoreferred to as the electrochemical paintbrush technique. This paintbrushsetup is believed to be useful in other high-resolution and non-highresolution electrochemical procedures.

Advantageously, the paintbrush technique does not require actual contactbetween the tip 130 and the ITO 12, but rather a uniform spacing ascontrolled by the z-axis feedback control circuit 330. This prolongs thelife of tip 130 and minimizes any degradation to ITO 12 prior to orafter copper deposition. This also permits correcting defectivedepositions while minimizing the likelihood of causing further defectsdue to contact between the tip 130 and the ITO 12. In this regard, withswitch SW2 open, computer 20 can operate STM 100 to inspect the ITOlayer 12 and measure the copper that has been deposited, or locate aparticular location in a given pattern, for example, to verify thecorrectness of the deposition pattern or to repair a portion of thepattern that was omitted or incorrectly applied. A correction may bemade at an identified site by closing switch SW2 and either applyingadditional copper dabs, if appropriate, or reversing the currentpolarity while the tip 130 is at the area of the misapplied copper, sothat the copper incorrectly deposited on the ITO 12 may be placed backinto solution and ultimately onto tip 130 (for redeposit onto eitheranother area of ITO 12 or copper electrode 700). Thus, a mask containingan error can be repaired by reversing the process by which themisapplied copper was originally deposited, rather than having toconstruct another mask. Similarly, if a circuit constructed according toa nanoscale mask turns out to be defective, the mask can be correctedrather than a completely new mask constructed. This is particularlyadvantageous when multiple or redundant circuits are to be patternedinto a semiconductor using a common mask, but it turns out that some ofthose circuits can be left out. By fixing the mask, leads to theunneeded or needed circuits can be permanently open circuited orshorted, as the case may be, without having to prepare a new mask.

EXAMPLE

A plastic substrate 14, was coated with a layer 12 of indium tin oxide(ITO) and used as the sample 10 in the apparatus described above. ITO isa transparent electrically conductive material and is well known. It haspreviously been used in electrochemistry experiments (See, e.g., Fu-RenFan et al., "Single Molecule Electrochemistry", Journal of the AmericanChemical Society, V. 118, (Oct. 9, 1996) pp. 9669-9675. ITO is commonlyused as the front surface electrode in liquid crystal displays andelectrochromic products, such as automatically darkening rear viewmirrors used in automobiles. The sample of ITO used in this example wasobtained from an electroluminescent strip in a photocopier machine. Asrecommended elsewhere (e.g., Feifer, Experimental Chemistry: The Howsand Whys of Chemistry, Arco Publishing Co., New York, 1975), the platingsolution 50 was an electrolyte having a 0.31M copper sulfate solutionwith 4.0 grams/liter of laboratory-grade gelatin dissolved in it toincrease the uniformity of the deposits. The ITO layer 12 wasapproximately 50 μm thick. The plastic substrate 14 was made ofplexiglass, and was optically transparent.

The experiment started with switch SW2 open, and the tip 130 approachingthe sample 10. As the tip 130 approached the ITO layer 12, theoscillations of amplifier A30 had a higher and higher frequency. If thetip 130 touched the ITO 12, the oscillations stopped. When the tip 130was positioned so that it almost touched the ITO 12, having oscillationsof approximately 500 Hz, and the switch SW2 was closed, copper startedto come out of solution on the ITO 12. Patterns are drawn on the ITO 12with the copper deposits by applying voltages to the x and y piezotransducers 140x and 140y to obtain a raster scan. In this regard, thetriangular wave generators discussed above in raster scan circuit 360are used. The paintbrush control circuit 500 is then operated to applyor not apply current to "paint" a plurality of dabs of copper in apredetermined pattern onto a plurality of areas of the ITO 12. Thepaintbrush current control may be achieved by opening and closing switchSW2 at appropriate times to deposit or not deposit a dab of copper on agiven area according to the pattern to be formed, or by drawing thepattern as the tip 130 traces out the pattern in a non-raster scan mode,similar to an ETCH-A-SKETCH toy (ETCH-A-SKETCH) is a trademark of OhioArts) except that the tip can be moved from one area to another withoutdepositng material therebetween. Thus, a pattern to be deposited on theITO 12, one dab 702 at a time, can be programmed into computer 20 andformed in sample 10. The data can be stored as timing intervals for thesquare wave generators and switch SW2. Alternatively, a bit map of x, ycoordinates and switch SW2 positions, or a sequence of x, y coordinatesand switch SW2 positions, can be used to define the pattern in memory.

"Before" and "after" scans of the actual copper deposits made in thisExample verify that copper deposition takes place. FIG. 8A shows an STMscan of the ITO surface before any copper deposition. FIG. 8B shows anSTM scan of the ITO surface after copper deposition has occurred asdescribed above. The constant current scans were obtained with atunneling current of 2 nA, and a bias voltage of 500 mV. The ITO used inthe experiment was removed from an electroluminescent strip, and it isbelieved that the removal of the ITO from the strip formed the ridges inthe image illustrated in FIG. 8A. Referring to FIG. 8B, it is noted thatthe ridges have been filled in by the copper deposited. The unitsdepicted of position and height are in nanometers, and are to scale inthree dimensions.

Additional Applications of the Electrochemical Paintbrush

The electrochemical paintbrush circuit and technique has manyapplications in addition to the manufacture of masks for near-fieldphotolithography. By reversing the direction of the current through thetip, the electrochemical paintbrush could remove material from a surfacewith a very high spatial resolution. The circuit could be used to modifypreexisting photolithography masks, either by fixing broken traces or byremoving unwanted material. This also gives circuit designers a lowercost option to prototyping integrated circuit designs because aparticular pattern can be revised and the same mask can thus evolve overtime.

The electrochemical paintbrush's ability to lift small quantities ofelectorchemically active substances off a surface also provides apowerful a method of surface analysis. Once a "dab" of analyte has beenlifted into the electrochemical solution by the paintbrush, standardchemical techniques could be used to identify or characterize theanalyte. This process should provide chemical sensitivity with extremelyhigh spatial resolution.

The electrochemical paintbrush may have uses in both inorganic andorganic chemistry. The paintbrush can deposit electrochemically activereagents with high resolution. Such deposits could provide usefulchemical sensors, as well as have applications in combinatorialchemistry.

Importantly, the electrochemical paintbrush is not confined to use inthe nanoscale range. Higher power versions of the circuit and largerdimensional amounts of material could be used in industrialapplications, such a plating a large pattern of one metal onto another.Further, when run in reverse polarity at high power, the electrochemicalpaintbrush could be used to mill parts from a solid block of metal. Innon-nanoscale applications, the STM 100 and its electrochemical tip 130can be replaced with a more conventional platinum electrode, havingthereon an insulated coating (e.g., parrafin) and an exposed tip thatprovides the desired spatial resolution in an electrolytic solution, forthe size of the dab to be deposited or removed.

High spatial resolution deposits on transparent ITO may have usefuloptical properties. Sub-wavelength deposits could be used to creatediffraction gratings and optical filters. For certain optical uses, thematerial deposited on ITO need not be an opaque metal, but could be anyelectrochemically active material with desirable optical properties.

Near-Field Photolithography

A near-field scanning optical microscope (NSOM) is a scanning probemicroscope where an extremely fine fiber-optic strand is scanned overthe surface of a sample. Because the fiber-optic strand in an NSOM iswithin 10 nm of the sample, diffraction does not limit the imagingresolution. NSOMs have been used to create images of a size down to asingle molecule (See, for example, M. Nieto-Vesperinas and NicolasGarcia (eds.), Optics at the Nanometer Scale: Imaging and Storing withPhotonic Near Fields, (Kluwer Academic, Boston, 1996)("Nieto-Vesperinas-Garcia"); Courjon et. al., "Instrumentation in nearfield optics" in Nieto-Vesperinas-Garcia, pp. 105-117; Betzig et al.,"Single molecules observed by near-field scanning optical microscopy"Science, V. 262 (Nov. 26, 1993) pp. 1422-5; Collins, "Near-field opticalmicroscopes take a close look at individual molecules" Physics Today, V.47 (May 1994) pp. 17-20; Hwang et al., "Nanoscale complexity ofphospholipid monolayers investigated by near-field scanning opticalmicroscopy" Science, V. 270 (Oct. 27, 1995) pp. 610-14; and Zenhausen etal., "Scanning interferometric apertureless microscopy: optical imagingat 10 angstrom resolution" Science, V. 269 (Aug. 25, 1995) pp. 1083-5.

Several authors have used an STM to create electrochemically nanoscalefeatures on surfaces. See, e.g., Gewirth et al, Nanoscale Probes of theSolid/Liquid Interface, (Kluwer Academic, Boston, 1995) and the articlestherein by Lagraff et al., "AFM studies of copper solid-liquidinterfaces," pp. 83-101; Nichols, "Scanning probe microscopy studies ofcopper electrodeposition," pp. 163-182, Wenjie Li et. al.,"Electrochemical deposition of metal nano-disk structures using thescanning tunneling microscope," pp. 183-192; and Fan et al., "SingleMolecule Electrochemistry", Journal of the American Chemical Society, V.118, (Oct. 9, 1996) pp. 9669-9675). Others have used an NSOM to patternphotosensitive surfaces with a resolution of down to 60 nm. See, e.g.,Ambrose et al., "Alterations of single molecule fluorescence lifetimesin near-field optical microscopy" Science, V. 265 (Jul. 15, 1994) pp.364-7; Madsen et al., "Surface modifications via photo-chemistry in areflection scanning near-field optical microscope" inNieto-Vesperinas-Garcia, pp. 263-275; and J. Massamell et. al. "Writingof nanolines on a ferroelectric surface with a scanning near fieldoptical microscope" in Nieto-Vesperinas-Garcia, pp. 181-190. While STMand NSOM patterning methods have high resolution, they both have thedisadvantage of being serial in nature. That is, the STM or NSOM tipacts like a pencil, only able to create one feature at a time. This ismuch too slow for practical applications in nanoscale manufacturing,especially semiconductor microchip production, as recognized in "Thelimits of lithography" Scientific American, (September 1995), p. 66; andStix, "Toward `point one`" Scientific American (February 1995), pp.90-5.

Advantageously, it has been recognized by the inventor that there existsa new field of lithographic technology, that of near-fieldphotolithography, which can be implemented in a commercially acceptableand useful manner. Near-field photolithography as contemplated by theinventor combines certain aspects of the STM and NSOM structures andtechniques in an advantageous manner that is capable of higher-speednanoscale patterning. In accordance with the present invention, fornear-field photolithography, an STM deposits a pattern of copper orother suitable opaque materal that is electroplateable, e.g., gold,silver, tin, zinc, nickel, chromium etc., on a transparent ITOelectrode. The ITO patterned with copper is then used as aphotolithographic mask. With reference to FIG. 9B, the mask 800 isdirectly placed against a photosensitive substrate, e.g., asemiconductor chip 804 or wafer, coated with a light sensitive resist802 and exposed to a light source. Preferably, the opaque pattern isplaced in touching contact with the resist coating. The light shiningthrough the mask creates a copy of the mask's pattern on thephotosensitive material which can then be etched away (see semiconductor804'). Each mask could be used multiple times, to create many copies ofa pattern, just as in the case of a conventional mask having adimensional resolution of 0.2 micrometers or greater. However, becausethe mask of the present invention is in close proximity or directcontact with the resist coating on the substrate, the light shiningthrough the mask is still in the near-field when it hits the resistcoating on the substrate. Near-field resolution is not Abbe-diffractionlimited; therefore, it is possible to create features that are muchsmaller than the wavelength of light used in the photo lithographicprocess. Consequently, by creating a photolithographic mask using theSTM 100 of the present invention, which has a nanoscale resolution,near-field photolithography can be used to obtain the same highresolution (small dimensions) of NSOM patterning, and yet retain thespeed and volume of production of conventional photolithography, bymoving the photolithographic mask of the present invention into thenear-field. Near-field photolithography thus offers a solution to theresolution problems existing in conventional photolithography. Compareto FIG. 9A, where the mask 900 is spaced from the photoresist 902, andlenses 901 are interposed therebetween to focus an image on photoresist902, which is then processed to etch semiconductor 904.

Advantageously, too, near-field photolithography would not be so slow asthe current efforts using microscopes to make nanoscale structures,because a copper-on-ITO template, once created, could be used manytimes. Moreover, a copper-on-ITO template can be used to create an evenlarger template by a step and expose, near-field, photolithographicprocess, so as to create a "super" mask or reticle having a dimensionsuitable to expose an entire semiconductor wafer in a single exposure.

Near-field photolithography, although in its infancy, is believed to bea viable and valuable technology. Surfaces to be patterned by near-fieldphotolithography should first be treated to be extremely flat, so thatdiffraction that might otherwise arise from excessive spacing betweenthe mask pattern and the semiconductor substrate will not come intoplay. The spacing is preferably maintained at less than 100 nanometers(more preferably less than 50 nanometers, with touching contactpreferred. Further, the stability of the deposits of copper on ITOshould be maintained and, as noted other electrochemically transferablematerials, such as silver, gold, tin, zinc, nickel, chromium, aluminum,molybdenum, cadium and the like, may be well-suited for use in place ofcopper, and other transparent conductive layers 12 may be well-suitedfor use in place of ITO. Further, alloys may be used, as may surfacetreatments of the conductive material, e.g., hydrogen passivation, ornitriding. Suitable photosensitive materials ("resists") used on thesubstrate to be exposed are those which will undergo a useful changewhen exposed to low levels of light, which may require some empiricalstudy before a widespread commercially acceptable standard is developed.Once these parameters have been selected, which are believed to bewithin the abilities of a person of ordinary skill in the relevant arts,the optical, electronic, and mechanical properties of materialspatterned with near-field photolithography are expected to provide newstructures which have a wide variety of applications in thesemiconductor and integrated circuit manufacturing industry, as well asopen up new areas of further research.

It is particularly envisioned that nanoscale semiconductor circuits canbe formed with circuit elements as small as 10 to 100 nanometers, byusing near field photolithographic masks and near field photolithographyto form the pattern in a semiconductor, such that the semiconductor isotherwise processed in the known manner to dope, oxidize, and etch thesemiconductor to form integrated circuits in the otherwise conventionaland well known manners. This can lead to a reduced size of integratedcircuits, and all of the benefits attendant thereto, e.g., savings inmanufacturing costs, materials and labor, and increased effectiveyields.

It also is believed within the scope of the invention to generate anx-ray opaque mask on an x-ray transmissive substrate by appropriateselection of a substrate, e.g., quartz, and depositing thereonelectrochemically a pattern by an appropriate material being selected inplace of copper. As a result, near field x-ray lithography also may beachieved to produce semiconductor circuits.

It also is believed to be within the scope of the invention to performnear field photolithography based on using nanoscale masks formed bynon-electrochemical techniques, e.g., electron beam or x-ray processes.

One skilled in the art will appreciate that the present invention can bepracticed by other than the described embodiments and in applicationother than those described herein, which are presented for purposes ofillustration and not of limitation.

I claim:
 1. A method for patterning an electrically conductive materialcomprising:a) providing an inert electrode covered by an insulator andhaving an exposed end; b) mounting said inert electrode on an actuatormovable in three dimensions, including an x-y plane and a z axis; c)providing a consumable electrode comprising an electroplatable material;d) immersing the electrically conductive material and at least a portionof each of said inert electrode and said consumable electrode in asolution containing ions of said electroplatable metal; e) passing afirst current between said consumable electrode and said exposed end ofthe inert electrode and depositing on said exposed end a first amount ofelectroplatable material; f) positioning said inert electrode exposedend a distance from an area of said electrically conductive material;and g) passing a second current between said inert electrode exposed endand said area of the electrically conductive substrate and depositing onsaid area the first amount of electroplatable material, wherein step f)occurs before or after step e).
 2. The method of claim 1 furthercomprising repositioning said inert electrode relative to saidelectrically conductive material and repeating steps e), f) and g) todeposit a plurality of first amounts to create a pattern on a differentarea of said electrically conductive material.
 3. The method of claim 2wherein each step g) further comprises depositing a first amount ofmaterial having a nanoscale resolution.
 4. A method of removing anelectrochemically active material that is a part of or in contact withan electrically conductive material, comprising:a) providing anelectrode having an insulated coating and an exposed tip; b) mountingsaid electrode on an actuactor movable in three dimensions, including anx-y plane and a z-axis; c) immersing the electrochemically activematerial and at least a portion of each of said electrode exposed tip inan aqueous electrochemical solution containing an ionic form of anelectroplatable material; d) positioning the electrically conductivematerial in an x-y plane relative to the electrode exposed tip so that afirst area of said electrochemically active material is aligned with andspaced from said tip; e) passing a first current between said electrodeexposed tip and said electrically conductive material and causing atleast a portion of said first area of said electrochemically activematerial to go into solution; f) providing a second electrode; and g)passing a second current between said electrode exposed tip and saidsecond electrode and depositing an amount of said electrochemicallyactive material on said second electrode.
 5. The method of claim 4further comprisingrepositioning said electrode exposed tip relative tosaid electrically conductive material in said x-y plane so that adifferent area of said electrically conductive material is aligned withand spaced from said exposed tip and passing a second current betweensaid exposed tip and depositing said portion of the electrochemicallyactive material on said different area.
 6. The method of claim 5 furthercomprising performing steps d and e to modify a pattern of aphotolithographic mask.
 7. The method of claim 6 wherein step e) furthercomprises passing a first current for a time to remove an amount ofelectroplatable material having a nanoscale dimension.
 8. The method ofclaim 4 wherein the electrochemically active material is anelectroplatable material, the electrically conductive material is indiumoxide, and the electroplatable material is deposited on said indiumoxide in a pattern forming a photolithographic mask.